Brick Chimneys – Q&A’s

  1. What causes their deterioration?
  2. What can you do to prolong them?
  3. What you should know before you repair.
  4. When is it time to rebuild your chimney vs. repoint?
  5. Conclusion


1. What causes their deterioration?

Quick answer: Freezing water/moisture.

Everybody knows that a roof needs replacing, it’s just as common as replacing the tires on your car. That’s because these are the things that receive the brunt of all weather conditions. There are no shingles above a chimney to protect it like there are above the walls of your home. Think about it: If your chimney is all that’s standing above the roof, then it’s going to get wet, frozen and warm over and over again. It’s these cycles that take the biggest toll on chimneys. Not to mention the purpose of the chimney itself is usually to vent some kind of exhaust. Gas, wood and oil fumes produce hydrogen sulfide. If the chimney liner ever leaks, cracks, deteriorates or fails in any way, you’ve now got an interior source of damaging moisture in the form of condensation to make things worse.

Photo Below – Chimney with a deteriorated gas boiler liner causing the spread of efflorescence through natural gas exhaust.


2. What can you do to prolong your chimney?

Quick answer: Inspect and act quickly by calling a qualified mason.

Usually the first place to look is the top of the chimney, the chimney cap or crown. You’re looking for cracks where water could enter. If you have a concrete cap, you’ll want to look to see that it has at least 2 inches of overhang all the way around the top layer of brick and that a drip edge line is present beneath the overhang at a minimum 1 inch distance from the brick face. For chimneys without a concrete cap, you are at greater risk of deterioration due to water run down versus shedding. If you have deterioration elsewhere on your chimney, begin looking for evidence of water. Common areas are where roof lines meet the chimney, leaky eaves and downspouts or near the flashings. Once you’ve determined where the water is, you can take necessary steps to avoid further or future deterioration, especially after a repair to your chimney is made. Water repellents, sealers and paint products are NOT recommended ways to prolong any masonry because you are preventing the porous masonry material from breathing as is intended/designed. If your chimney was built correctly, it will last many decades without needing any maintenance. If you see damage on your chimney and don’t know why, let someone experienced answer your questions.

Photo Below – Triple chimney failure 1.) Top of chimney has no concrete cap. 2.) Evidence that incorrect mortar type was used. 3.) Leaking eavestrough below roof.


3. What you should know before you repair.

Quick answer: Learn why it failed where it did and ask how it’s going to be addressed to prevent re-occurrence.

Some of you reading this may just be interested enough to care about this topic, if you’re one of them, it’ll give you piece of mind for your investment. We know water (and freezing) is the root cause of deterioration, but why only sometimes does it cause problems? A chimney has a number of rules that should be followed in order to be built correctly. The photo below illustrates a basic chimney and some of the small yet important features that should be included when constructing or re-constructing a long lasting chimney.

Further to this illustration, other major factors need to be considered when building any masonry structure. Some would include: the type or “strength” of mortar being used with the corresponding brick/stone material. More on mortar types will be discussed elsewhere in this blog. What style of joint the mortar is being tooled to, as there are many, concave is considered the best for longevity.

Photo below – Chimney Anatomy


4. When is it time to rebuild your chimney vs. repoint?

Quick answer: This can be subject to speculation depending on the severity. Generally we rebuild when there are loose or spalling bricks, leaning chimney, deep holes in mortar, obvious shifting or bulging, crumbling/soft mortar through the whole depth of the brick or stone, or if it has been previously repointed. Repoint when bricks are solid and only surface mortar has deteriorated.

In some cases, a chimney can be repointed rather than rebuilt. If all the bricks are in good solid condition, you may just have surface mortar deterioration. If you’ve caught it at the right time you may only need to repoint, this is the process of removing the existing mortar to a depth of around an inch deep, cleaning out the debris and then inserting new properly specified repointing mortar into the empty joints. It is best to repoint the chimney all the way around starting from a point just lower than the most degraded area. This allows for a total uniform strength, colour and consistency throughout all surrounding areas of the chimney. Rebuilding and repointing can be combined together. Many times only the portion of chimney above the roof needs reconstruction and below that point can be repointed depending on the situation. An experienced restoration mason can tell by looking at the conditions of the structure and provide the best solution.

Photo Below – A possible chimney fit for repointing.



This information is only meant to provide some knowledge regarding common chimney conditions and practices. Always get the advise of a professional before making any judgement based on this information. Go with your gut when getting estimates. If you get the feeling a contractor is avoiding doing the job the right way, they may just be looking for the quickest way in and out with your poor investment. Be wise and research your situation along with the contractors you plan to call on for estimates.